Maedi visna can hit sheep farmers’ profits

Maedi visna (MV) may not be the disease of the moment, but lack of awareness of the disease can result in substantial financial losses

This is according to commercial sheep producer, Andrew Hodgson and SAC vet, Graham Baird who addressed visitors to South Sheep, Chilbolton Down Farm, Stockbridge,

In fact MV has reduced output in Mr Hodgson’s flock of 1500 Masham ewes by 20-40% and reduced annual turnover by £30,000-£40,000.

The problem with MV is that clinical signs of the disease are often not seen until 50% of sheep are infected, explained Mr Baird. “MV virus has a long incubation period, meaning it can take years for the disease to develop in a flock.”

And this was the case for Mr Hodgson, Cheverton Farm, Isle of Wight, where it took more than seven years for the disease to become apparent.

“We always buy our stock from a known source to prevent the risk of buying in disease, but following the 2001 foot-and-mouth outbreak, we purchased a group of Mule ewes locally – in hindsight, I can link MV back to these animals.”

The group were always hard work, with a high level of mastitis and consequently many were culled early. However, the symptoms these ewes showed were not seen again until seven years after they were bought.

“Before lambing in 2009, many single ewes were of low condition score – we had a lot of small lambs and reduced milk production, resulting in poor lamb growth rates.”

MV can manifest itself in a range of different ways, including weight loss, pneumonia, hind limb paralysis and mastitis, explained Mr Baird. And with no cure or vaccination available and total culling not an option for many commercial producers, prevention is key.

Once bloods identified MV as the cause of the problem, the disease could be attributed to other issues in the flock, including increased ewe mortality and lower returns from ewes, said Mr Hodgson.

“To control the disease we could have re- stocked completely, but this would have created an even higher disease risk.” Instead, the farm decided to undertake targeted blood testing and culling.

“We will continue to do this, while separating older and younger stock – hopefully this will lead to total eradication.”

To prevent MV from entering the flock, stock should be purchased from a clean source and fields double fenced to prevent nose to nose contact with neighbouring sheep, said Mr Baird.